Because if its hot it can burn your insides so if you even licked it it would still burn your insides so if you did eat it go to the emergency room right away but if you get it on your skin it will...
Tar paper is used as a moisture barrier between the plywood decking and the roofing materials.
A 400 square foot roll of 15# saturated felt will run from $12-$18, depending on your location.
Tar paper is the part that makes the roof waterproof. Shingles only protect the tarpaper from the elements.
If you had enough layers, yes.